The present invention relates to a new and improved method of, and apparatus for, measuring the distance between a primary station and a secondary station, each having an antenna for transmitting and receiving continuous wave signals modulated by a measuring signal, the distance at the primary station being determined as a magnitude proportional to the quotient of the phase difference between the measuring signals of the transmitted and received signals and the measuring signal frequency.
For measuring the distance between a primary station and a secondary station, there can be employed, apart from optical devices or radar-like devices operating in a pulse mode, also devices wherein the distance is determined by modulation of a microwave. One such type of prior art microwave-distance measuring system is disclosed, for instance, in the German literature entitled "Allgemeine Vermessungs-Nachrichten" February 1971, pages 50-60. It consists of two stations, each having a transmitter, a receiver, a parabolic antenna, a mixer, a control device, a measuring signal-source, and a response device. Additionally, the primary station is equipped with a phase measuring device and the secondary station with a pulse circuit as well as a synchronization circuit. This equipment is particularly suitable for measuring intermediate and large distances, since its range is hardly impaired by adverse weather and visual conditions. This state-of-the-art microwave distance measuring device operates in a manner such that after establishing a connection between both of the stations the carrier signal at each station is modulated by a measuring signal and transmitted as a measuring wave in the direction of the other station. Each station receives the delayed measuring wave of the other station and there is determined the momentary phase position with respect to the inherent transmitted measuring wave. The momentary phase position of the secondary station is further transmitted to the primary station in the form of an additionally modulated signal and at that location compared with its own phase position. Since the difference between the phase positions or phases determined at the primary station and secondary station is proportional to the distance, this difference is determined by the phase measuring device of the primary station, converted into a digital distance measuring result and then displayed.
The construction of such microwave-distance measuring device is relatively complicated, especially as concerns the secondary station which essentially consists of the same components as the primary station. Additionally, such secondary station is not readily portable owing to its relatively large weight.